TEMPORAL DYNAMICS OF CENTRAL AUDITORY PROCESSING

描述(申请人提供)：本研究计划的总体目标是调查序列中时间离散声音之间的时间间隔如何影响中枢听觉神经元的基本反应特性。在序列中产生的声音是大多数生物声学信号的共同之处，例如蝙蝠使用的生物声纳声音和包括语音在内的交流声音。最近对蝙蝠下丘(IC)的研究表明，随着声刺激频率的增加，神经元对声音序列的幅度选择性逐渐增加。初步研究表明，刺激率对IC单元在几个维度上的响应具有更全球性的影响，包括该单元的频率选择性。此外，在心理物理实验中，随着声音刺激率的增加，人类听者辨别声音级别细微差异的能力也会提高。因此，了解幅度和频率选择性随频率变化的机制不仅可以解释回声定位蝙蝠的行为表现，而且还可以促进我们对人类语音处理的理解。将解决三个具体目标。目的1是定量地表征IC中单个神经元在不同脉冲重复率下对声音频率的反应选择性，以验证频率选择性依赖于刺激速率的假设，即当以较高的重复频率呈现单音脉冲时，选择性更强。目的#2是确定在一个序列中改变幅度选择性所需的最小音脉冲数，以检验这样的假设，即在仅存在一个前面的声脉冲的情况下，IC神经元对声脉冲的幅度和频率选择性可以被增强。目的#3利用细胞外微离子导入技术和细胞内记录技术，研究单个中枢神经元突触后事件在幅度和频率选择性上的速率依赖性，以验证当声脉冲以较高的重复频率呈现时抑制比以较低重复频率呈现时更强的假设。

DESCRIPTION (provided by applicant): The overall aim of this research program is to investigate how the time interval between temporally discrete sounds in a sequence influences the fundamental response properties of central auditory neurons. Sounds produced in sequences are common to most bioacoustics signals such as the biosonar sounds used by bats and communication sounds including speech. Recent studies in the inferior colliculus (IC) of bats show a progressive increase in amplitude selectivity of neurons to sounds in a sequence when the rate of acoustic stimulation is increased. Pilot studies have revealed that the rate of stimulation has a more global impact on an IC unit's responses across several dimensions, including the unit's frequency selectivity. In addition, the ability of human listeners to discriminate small differences in sound level improves with increased rate of acoustic stimulation during psychophysical experiments. Therefore, understanding the mechanisms that underlie rate-dependent changes in amplitude and frequency selectivity could not only explain behavioral performance of echo locating bats, but it could also advance our understanding of speech processing in humans. Three specific aims will be addressed. Aim #1 is to characterize quantitatively the response selectivity's of single neurons in the IC to sound frequency when the stimuli are presented at different pulse repetition rates to test the hypothesis that frequency selectivity is dependent upon the rate of stimulation, i.e., the selectivity is greater when the tone pulses are presented at higher repetition rates. Aim #2 is to determine the minimum number of tone pulses in a train required for a change in amplitude selectivity to test the hypothesis that the amplitude and frequency selectivity's of IC neurons to a sound pulse can be enhanced in the presence of as few as one preceding sound pulse. Aim #3 is to study the postsynaptic events that underlie the rate-dependence in amplitude and frequency selectivity's in single IC neurons, using extracellular microiontophoretic injection techniques and intracellular recording to test the hypothesis that inhibition is more robust when sound pulses are presented at high than low repetition rates.